1. Field of the Invention
The present invention relates to a sheet processing apparatus for sorting the sheets discharged from an image forming apparatus or the like, binding the sorted sheets, and stacking the bound stacks of sheets; in other words, the present invention relates to a sheet processing apparatus for processing sheets after the formation of an image thereon.
2. Related Art
There have long been known sheet processing apparatuses which sort the sheets discharged from an image forming apparatus after the formation of an image thereon, bind the sorted sheets, and stack the bound stacks of sheets.
These sheet processing apparatuses are structured so that they can be connected to a plurality of image forming apparatuses different in performance.
Generally, a sheet processing apparatus is combined with an image forming apparatus to create a printing system, or is combined with two or more image forming apparatuses different in function or performance, creating printing systems different in function and performance. Thus, normally, the specifications of the motors and motor drivers of a sheet processing apparatus, and the values of the electric currents for driving the motors, are set in accordance with the specifications of the image forming apparatuses which are currently fastest in processing speed, or are set in anticipation of the possibility that it may be connected in the future, to image forming apparatuses which are much faster than the currently fastest image forming apparatuses. Therefore, in the case of a printing system created by connecting a sheet processing apparatus to an image forming apparatus inferior in processing capacity to the sheet processing apparatus, the processing speed of the sheet processing apparatus is faster than that of the image forming apparatus. In such a case, it does not occur that the sheet processing apparatus operates at its capacity. Thus, in such a case, in order to prevent the sheet processing from operating at an unnecessarily high performance level, to conserve energy, and to reduce noise, the amount of the electric current for driving the sheet processing apparatus, the revolutions of the motors of the sheet processing apparatus, etc., are reduced so that the performance of the sheet processing apparatus matches that of the image forming apparatus.
Japanese Patent Application Laid-open No. 7-264893, which relates to an image forming apparatus, a sheet processing apparatus connected thereto, and the stepping motors employed by the sheet processing apparatus, discloses a method for increasing the torque of the stepping motors by increasing the amount of the electric current supplied thereto, in response to the changes in load. Further, Japanese Patent Application Laid-open No. 9-190916, which relates to a solenoid, discloses another method for increasing the torque of a motor by increasing the amount of the electric current supplied thereto, in response to load.
However, the aforementioned methods suffer from the problem that as the amounts of the electric currents supplied to various driving systems are independently increased in response to their loads, the total electric power required by the printing system unexpectedly increases.
Further, in the case of a design in which the amount of electric current is increased in response to the loads measured by load measuring apparatuses, when the amount of the electric current required at a given moment by the printing system is greater than the sum of the maximum capacities of the driving systems of the printing system, the amount of the electric current cannot be increased to a target value, and therefore, the system is forced to operate at a reduced performance level, which is also problematic.
The present invention was made in consideration of the above described problems, and its primary object is to provide a driving apparatus for a sheet processing apparatus, systemized so that if an abnormality is detected in any of the driving systems of the driving apparatus, and the amount of the electric current being supplied to the driving system in which the abnormality was detected is at the maximum electric current limit thereof, the speed of the driving system in which the abnormality was detected is reduced, and one or more driving systems, other than the driving system in which the abnormality was detected, are increased in speed in the order of priority to compensate for the effect of the speed reduction of the driving system in which the abnormality was detected, so that even if an abnormality is detected in any of the driving systems, the driving apparatus is prevented from simply shutting down, and also so that the overall performance of the sheet processing apparatus is prevented from declining; so that abnormality detection is prohibited during sheet conveyance, making it possible for an abnormality of a driving means traceable to a sheet jam to be differentiated from an abnormality of a driving system itself by simple control; and so that it can be known by a remote control operator or a service person that the driving apparatus is operating in the mode in which the driving apparatus is prevented from shutting down, making it unnecessary to call for a service person when it is possible for the driving apparatus to automatically recover, reducing thereby the maintenance cost of the driving apparatus. Another object of the present invention is to provide a sheet processing apparatus having the above described driving apparatus, an image forming apparatus connectible to the sheet processing apparatus, and a system for controlling the apparatuses.